The present invention relates to alternators and regulators therefor, and especially, compact and efficient high output alternators and shunt regulators for such alternators which may use relatively low current rating switching devices.
In recent years, the demand for permanent magnet alternators which produce relatively high output currents has been increasing. Ordinarily, the output current of an alternator can be increased by increasing the size of the alternator, and especially, the cross sectional area of the wire or conductor which forms the windings of the alternator. Unfortunately, increasing the cross sectional area of the conductor which forms the windings has drawbacks. Firstly, as conductor size increases, the wire is more difficult to wind on the stator structure of the alternator, and particularly, the forces which must be exerted on the conductor during winding increases as conductor size increases. Furthermore, the resulting winding is not as compact or as efficient as a winding with a smaller conductor size. This is principally due to the fact that the space between the conductors on the stator structure increases in cross sectional area as the conductor size increases.
An ancillary problem associated with the increase in output of the alternator is the problem of regulation of the alternator output. A now widely used form of regulation of permanent magnet alternators is disclosed in the U.S. patent to Carmichael et al, No. 3,270,268, issued Aug. 30, 1966. According to the teachings of that patent, the output of the permanent magnet alternator is shunted on at least one half cycle of the output waveform so as to effectively reduce the battery charging current to near zero. On the opposite half cycle, the field created by the shunt current collapses to produce a magnetic flux in opposition to the permanent magnet flux tending to reduce the output of the alternator on the opposite half cycle. The aforementioned patent to Carmichael et al also teaches means for reducing the current through the shunt switching element during shunt regulation of the alternator in the form of a regulating winding which may be connected in series with output or load winding of the alternator during shunt regulation of the alternator.
The regulator of this invention also shunts the output of the alternator to regulate the alternator. However, novel means are disclosed for reducing the current through the switching element of the shunt regulator without the use of a regulating winding. This aspect of the present invention is particularly important where there is insufficient room on the stator structure for a regulating winding, or where a compact stator structure is desired.
The alternator of the present invention has a plurality of sets of windings which are connected in parallel for increasing the output current of the alternator without a corresponding increase in conductor size. For example, a twelve pole stator may have two sets of six windings or four sets of three windings, with each set being on respective sequential poles. As a further example, an eighteen pole stator may have three sets of six windings, again with the sets being on respective sequential poles.
In order to achieve the desired output voltages and currents of the alternator, the wire size or cross sectional area is selected to be one-half that normally used to provide the given output current, but the number of turns is doubled to account for the fact that the set is on one-half the number of poles. If four sets are used, the wire size is selected to be one-quarter that normally used, but the number of turns are quadrupled, again so as to compensate for the fact that each set is on a reduced number of poles. Hence, the winding wire size is reduced by a factor equal to the number of sets, and the number of turns is increased by a factor equal to the number of sets. Preferably, each set is wound on a like number of poles, e.g., the stator is divided into a plurality of equal segments of a like number of poles with each winding set being wound on a respective segment of the stator.
On actual experimentation, it has been found that the output current levels are actually increased relative to an alternator having one set of windings of full wire size and normal complement of turns. This increase in output current levels is believed to be attributable to the greater efficiency obtained by virtue of the closer coupling of the smaller wire to the stator pole structure. Other factors may also contribute to the increase output current levels which are not known at the present time to applicant.
The present invention also provides regulators which are especially suited for use with the high output alternators of this invention, and particularly, shunting-type regulators which provide relatively modest current levels through the shunt switching devices without the use of regulating windings. In a first embodiment, the battery is placed in opposition to the windings of the alternator on one half cycle of the output waveform to reduce the output current of the alternator and to reduce the regulating current of a shunt regulator on the other half cycle. In a second embodiment, each of the output windings are regulated using shunt regulators. The shunt regulators are connected so as to individually regulate the output windings and also shunt the output windings in a series connected mode. The individual and series regulation of the output windings is cooperative so that each switching element of the regulators carries one-half of the output current of the alternator. In still another embodiment, the battery is discharged through a series connection of the normally-parallel output windings. The output windings are further connected in series in shunt regulation of the output windings and a single one of the output windings is also individually shunt regulated. The cooperation of the various modes of regulation of the output windings reduces the current through the regulator switching elements.
Other features of the present invention will be apparent in view of the following detailed description of the preferred embodiments.